For the first time, scientists have pinpointed a chemical ‘switch’ that can reverse the "biological clock" by making human muscles younger and stronger .

As time passes, our muscles slowly lose their ability to regenerate. This not only occurs in the muscles of our arms, legs and torso but also the internal ones such as our hearts. As the muscles weaken, we lose strength, become less agile and eventually our organs fail leading to death.

However, all this can now be overturned - thanks to the breakthrough which implies a drug that rejuvenates old muscles and prevents young muscles from ageing can be created.
In the study, researchers have shown that the process appears to turn-off in elderly patients - preventing the fibres from repairing themselves so they begin to wither away, reports The Daily Express .
But when the switch is turned back on, it triggers a chain of events that allows muscles to rejuvenate. To reach the conclusion, researchers from the University of California at Berkeley carried out tests on tissue samples from around 30 healthy men. Half the volunteers were 21 to 24-year-olds and half aged between 68 and 74, reports The Daily Express .
Samples of tissue were surgically removed from the participants’ thighs. Then the volunteers had one of their legs immobilised in a cast for two weeks so their muscles began to waste. Following the removal of the casts, the men exercised with weights.
Then more tissue samples were removed three days and then four weeks later. When tests were carried out on these samples, the scientists found that during the exercise period the muscles of younger volunteers had four times more regenerative stem cells engaged in tissue repair than those of older participants. Old muscle also showed signs of damaging inflammation and scarring.
Dr Morgan Carlson, a member of the Berkeley research team, said: "The old muscle didn’t recover as well with exercise. This emphasises the importance of older populations staying active because the evidence is that for their muscle, long periods of disuse may irrevocably worsen the stem cells’ regenerative environment."
After understanding what happens when human’s age, scientists began to look at how to stop it happening.
After analyses, they found that a key protein is needed to allow muscle stem cells to get to work repairing tissue.
But in case of older people, the protein called mitogen-activated protein kinase, was missing.
However, when it was added to samples of elderly patients’ muscles, they began to repair. And when it was blocked in younger patients, they did not repair as well.
The team believes this protein and the switch it turns on and off, called Notch, will be the key for drug development in the future.